Heretofore it has been common to seal an end fitting into engagement with an elution column by mechanisms which require the use of tools such as wrenches and the like in order to make up and unmake the sealing arrangement. A conventional seal of this type is the compression fitting seal such as manufactured by Crawford Fitting Company of Cleveland, Ohio and sold under the trademark "Swagelok" or a similar seal made by Parker-Hannifin of Cleveland, Ohio. These compression fittings are quite reliable and rely on a metal to metal seal using a cone shaped ferrule which is driven into a cone shaped machined recess in an end fitting by an external nut threaded into or about the end fitting. In this way the ferrule is driven into the cone shaped recess which squeezes it into radial compression against the interposed tube to obtain a good metal-to-metal seal. While these fittings can be taken apart and reassembled satisfactorily, they require the use of wrenches and can be overtightened or insufficiently tightened depending upon the skill of the operator. It is very difficult to assess whether or not and when this type of seal has been made up to the proper amount.
Another type of seal utilizes a plastic cone shaped seal which is also arranged in a cone type configuration. However, the seal itself depends upon deformation of the plastic which may be of the polytetrafluoroethylene (Teflon) type. Such seals can be made up once but they are not reliable when disassembled and attempts are made to reseal using the same parts. Additionally, they require wrenches or other tools to make and break them. Unfortunately, polytetrafluoroethylene has a tendency to cold flow and such seals tend to lose their integrity over a period of time whether or not they are unmade.
As a last example, certain types of column end fitting seals in liquid chromatography utilize a metal-to-metal gasket which is interposed between the end fitting and the column sealing faces. While this provides a reliable seal the first time it is made, it cannot be unmade and reset many times without replacing the gasket. This type of seal also requires wrench type tools to make and unmake the same.
From the foregoing it can be seen that the existing seals each suffer from certain disadvantages, principally in the ability to be resealed and to be assembled and disassembled easily without the need for wrenches or other special tools. It will be appreciated that most columns of this type are relatively unsupported and that the difficulty of making and breaking seals arises in part from the necessity for the operator to have considerable physical dexterity in handling the apparatus which may be unsupported except by the attached semi-flexible capillary inlet and outlet tubing.
Furthermore, the aforementioned seals which operate utilizing cone shaped ferrules or other cone shaped seals to radially compress either the seal or deform the tube wall, operate at an angle to the liquid force which they are attempting to seal. As such, they are inherently mechanically inefficient since they operate at sealing force angles not aligned with the direction of pressure of the liquid being sealed, and do not lend themselves to possible operation by simple finger tightening of parts.
In addition to the foregoing the several components of the seals as described above comprise a plurality of parts which have to be assembled together in a particular order, certain of the parts being so small that they are readily misplaced. Because of this and the uncertainty of leakage on reconnection it has often been found necessary to replace the seal as a standard precautionary measure.
There is therefore a need for a new and improved elution column seal and holder assembly for use in liquid chromatographs.